1. Field of the Invention
This invention relates to a collet chuck and a collet used therein and more particularly to an oil feeding collet chuck wherein cutting oil is supplied to a tool fitted in a collet chuck from an oil passage in a main body of the chuck and to a collet for the chuck.
2. Description of the Prior Art
A main body 1c of a conventional collet chuck Ac comprises a tapered hole 2c, at one end thereof, to put a collet 9c therein and an inside oil passage 4c communicating with the tapered hole 2c, as shown in FIG. 7. The outside surface of the collet 9c is made in a tapered form to fit closely in the tapered hole 2c. The collet 9c includes a groove 17c at the front end portion (the large radius side) of the outside surface thereof, a fitting flange 18c contiguous to the groove 17c and a tool holding hole 13c formed in the axial portion thereof. A plurality of axially long radial slits 14c are formed in the collet 9c at circumferential suitable intervals and terminate in an annular base portion 12c at the rear end portion (the small radius side) of the collet 9c and a loose hole 34 is formed in this base portion 12c. All the radial slits 14c are open at the front end of the collet 9c and communicate with the loose hole 34 and the tool holding hole 13c. The axially long radial slits 14c make possible the radial constriction of the collet 9c. The collet chuck Ac is provided with a clamp member 20c to press the collet 9c into the tapered hole 2c. Cutting oil is supplied to a tool 28c fitted in the tool holding hole 13c from the oil passage 4c through the loose hole 34 and the radial slits 14c.
When the cutting oil is supplied at a constant flow rate, the axial speed of the cutting oil flowing out of the front end of the collet 9c is inversely proportional to the sum of those cross-sectional areas of all the radial slits 14c which are perpendicular to the axis of the collet 9c at the front end of it. This sum is considerably large for the radial slits 14c provided for the purpose of constricting the collet radially. Accordingly, the axial speed of the cutting oil is rather small and the cutting oil can not be sufficiently supplied to a tip 29c of the tool 28c where the cutting oil is most required. When the chuck Ac is rotated at a high speed, the cutting oil subject to the centrifugal force due to rotation will flow radially out of the front end of the collet 9c as well and the supply of the cutting oil to the tool 28c is the more insufficient. Furthermore, the cutting oil together with scrap and dust metals contained therein enters the grooves for balls 25c formed in a main body 21c of a clamp member 20c and the main body 21c sometimes is unable to rotate.
In another conventional collet chuck Ad shown in FIG. 8, an oil duct 32d is formed, along the axis of a tool 28d, from a tip 29d of the tool 28d to the rear end of it. In all the figures of the present specification, same reference numerals represent same or equivalent members and accompanying alphabets a through d are used in order to discriminate different examples and embodiments. The oil duct 32d communicates directly with an oil passage 4d at the rear end of the tool 28d and a gum seal 35 prevents the cutting oil from leaking towards radial slits 14d. In this collet chuck, the cutting oil is supplied sufficiently to the chip 29d of the tool 28d through the oil duct 32d.
However, when the chuck is used for a long time and the gum seal is damaged, the cutting oil begins to leak to the radial slits and the cutting oil again is insufficiently supplied.